Disturbance of hepatocyte growth and metabolism in a hyperammonemia microenvironment.

BACKGROUND: We found through previous research that hyperammonemia can cause secondary liver damage. However, whether hepatocytes are target cells of ammonia toxicity and whether hyperammonemia affects hepatocyte metabolism remain unknown. AIMS: The purpose of the current study is to examine whether the hepatocyte is a specific target cell of ammonia toxicity and whether hyperammonemia can interfere with hepatocyte metabolism. METHODS: Cell viability and apoptosis were analyzed in primary hepatocytes and other cells that had been exposed to ammonium chloride. Western blotting was adopted to examine the expression of proteins related to ammonia transport. We also established a metabolomics method based on gas chromatography-mass spectrometry to understand the characteristics of the hepatocyte metabolic spectrum in a hyperammonemia microenvironment, to screen and identify differential metabolites, and to determine the differential metabolic pathway. Different technologies were used to verify the differential metabolic pathways. RESULTS: Hepatocytes are target cells of ammonia toxicity. The mechanism is related to the ammonia transporter. Hyperammonemia interferes with hepatocyte metabolism, which leads to TCA cycle, urea cycle, and RNA synthesis disorder. CONCLUSIONS: This study demonstrates that hepatocyte growth and metabolism are disturbed in a hyperammonemia microenvironment, which further deteriorates hepatocyte function.

Switching from Fatty Acid Oxidation to Glycolysis Improves the Outcome of Acute-On-Chronic Liver Failure.

Acute-on-chronic liver failure (ACLF) has a high mortality rate. Metabolic reprogramming is an important mechanism for cell survival. Herein, the metabolic patterns of ACLF patients are analyzed. An in vitro model of ACLF is established using Chang liver cells under hyperammonemia and hypoxia. A randomized clinical trial (ChiCTR-OPC-15006839) is performed with patients receiving L-ornithine and L-aspartate (LOLA) daily intravenously (LOLA group) and trimetazidine (TMZ) tid orally (TMZ group) based on conventional treatment (control group). The primary end point is 90-day overall survival, and overall survival is the secondary end point. By analyzing metabolic profiles in liver tissue samples from hepatitis B virus (HBV)-related ACLF patients and the controls, the metabolic characteristics of HBV-related ACLF patients are identified: inhibited glycolysis, tricarboxylic acid cycle and urea cycle, and enhanced fatty acid oxidation (FAO) and glutamine anaplerosis. These effects are mainly attributed to hyperammonemia and hypoxia. Further in vitro study reveals that switching from FAO to glycolysis could improve hepatocyte survival in the hyperammonemic and hypoxic microenvironment. Importantly, this randomized clinical trial confirms that inhibiting FAO using TMZ improves the prognosis of patients with HBV-related ACLF. In conclusion, this study provides a practical strategy for targeting metabolic reprogramming using TMZ to improve the survival of patients with HBV-related ACLF.

[Specific expression of CPS-II in hyperammonemia-injured liver cells].

OBJECTIVE: To study the CPS-II mechanism underlying the pathological process of elevated blood ammonia leading to liver injury. METHODS: An in vitro hyperammonemia hepatocyte cell model was constructed by exposure to various concentrations of NH4Cl. The subsequent changes to cellular morphology were observed by microscopy. to cell apoptosis were determined by flow cytometry, and to mRNA and protein expression of CPS-II were examined by real-time PCR and western blotting, respectively. RESULTS: Exposure to NH4Cl led to dose-dependent morphological damage, apoptosis and necrosis of the hepatocytes. The apoptosis rate was significantly higher for the high-dose group than for the control (no exposure) group (24.7% ± 2.39% vs. 4.1% ± 0.78%, q =8.06, P less than 0.05). Expression of the CPS-II mRNA was significantly elevated in response to NH4Cl exposure (vs. the control group; F=191.881, P < 0.05).The CPS-II mRNA expression level increased with increasing NH4Cl concentration (grey values: 1.040 ± 0.045, 1.641 ± 0.123, 2.285 ± 0.167 and 3.347 ± 0.124, respectively). The CPS-II protein expression level was also significantly enhanced in response to the NH4Cl exposures (CPS-II protein and internal GAPDH grey value ratios: 0.099 ± 0.0130, 0.143 ± 0.025, 0.161 ± 0.036 and 0.223 ± 0.042, respectively; t=3.825, 3.968 and 6.908, P less than 0.05). CONCLUSION: CPS-II mRNA and protein expression levels become elevated with increase in the NH4Cl concentrations, suggesting that in addition to the urea cycle, CPS-II may play an important role in the ammonia metabolism under the condition of hyperammonemia.

Ammonium chloride inhibits autophagy of hepatocellular carcinoma cells through SMAD2 signaling.

Autophagy is a cellular degradation process for the clearance of damaged or superfluous proteins and organelles, the recycling of which serves as an alternative energy source during periods of metabolic stress to maintain cell homeostasis and viability. The anti-necrotic function of autophagy is critical for tumorigenesis of many tumor cells, including hepatocellular carcinoma (HCC). However, the underlying mechanism is not clarified yet. Ammonium chloride (NH4Cl) is a well-known autophagy inhibitor, whereas its interaction with SMAD2 signaling pathway has not been reported previously. Here, we show that NH4Cl significantly inhibited rapamycin-induced autophagy in HCC cells through decreasing the levels of Beclin-1, autophagy-related protein 7 (ATG7), p62, and autophagosome marker LC3 and significantly decreased the level of phosphorylated SMAD2 in rapamycin-treated HCC cells. In order to find out whether NH4Cl may inhibit the autophagy in rapamycin-treated HCC cells through inhibition of SMAD2 signaling, we used transforming growth factor ß1 (TGFß1) to induce phosphorylation of SMAD2 in HCC cells. We found that induction of SMAD2 in HCC cells completely abolished the inhibitory effect of NH4Cl on rapamycin-induced autophagy in HCC cells, suggesting that NH4Cl inhibits autophagy of HCC cells through inhibiting SMAD2 signaling.

Hyperammonia induces specific liver injury through an intrinsic Ca2+-independent apoptosis pathway.

BACKGROUND: Numerous pathological processes that affect liver function in patients with liver failure have been identified. Among them, hyperammonia is one of the most common phenomena.The purpose of this study was to determine whether hyperammonia could induced specific liver injury. METHODS: Hyperammonemic cells were established using NH4Cl. The cells were assessed by MTT, ELISA, and flow cytometric analyses. The expression levels of selected genes and proteins were confirmed by quantitative RT-PCR and western blot analyses. RESULTS: The effects of 20 mM NH4Cl pretreatment on the cell proliferation and apoptosis of primary hepatocytes and other cells were performed by MTT assays and flow cytometric analyses. Significant increasing in cytotoxicity and apoptosis were only observed in hepatocytes. The cell damage was reduced after adding BAPTA-AM but unchanged after adding EGTA. The expression levels of caspase-3, cytochrome C, calmodulin, and inducible nitric oxide synthase were increased and that of bcl-2 was reduced. The Na+-K+-ATPase activities in hyperammonia liver cells was no signiaficant difference compaired with the control group, but was decreased in astrocytes. NH4Cl pretreatment of primary hepatocytes promoted the activation of mitochondrial permeability transition pores and the mitochondria swelled irregularly. CONCLUSIONS: Hyperammonia induces specific liver injury through an intrinsic Ca2+-independent apoptosis pathway.

Ammonia-induced energy disorders interfere with bilirubin metabolism in hepatocytes.

Hyperammonemia and jaundice are the most common clinical symptoms of hepatic failure. Decreasing the level of ammonia in the blood is often accompanied by a reduction in bilirubin in patients with hepatic failure. Previous studies have shown that hyperammonemia can cause bilirubin metabolism disorders, however it is unclear exactly how hyperammonemia interferes with bilirubin metabolism in hepatocytes. The purpose of the current study was to determine the mechanism or mechanisms by which hyperammonemia interferes with bilirubin metabolism in hepatocytes. Cell viability and apoptosis were analyzed in primary hepatocytes that had been exposed to ammonium chloride. Mitochondrial morphology and permeability were observed and analyzed, intermediates of the tricarboxylic acid (TCA) cycle were determined and changes in the expression of enzymes related to bilirubin metabolism were analyzed after ammonia exposure. Hyperammonemia inhibited cell growth, induced apoptosis, damaged the mitochondria and hindered the TCA cycle in hepatocytes. This led to a reduction in energy synthesis, eventually affecting the expression of enzymes related to bilirubin metabolism, which then caused further problems with bilirubin metabolism. These effects were significant, but could be reversed with the addition of adenosine triphosphate (ATP). This study demonstrates that ammonia can cause problems with bilirubin metabolism by interfering with energy synthesis.